With the recent trend toward higher degrees of integration and higher densities in semiconductor integrated circuits, an exposure tool for semiconductor device production employing an ArF excimer laser (193 nm) as an exposure light source has come to be used for producing a fine and precise circuit pattern by photolithography. In the optical system of this apparatus, a synthetic quartz glass body having excellent light-transmitting properties is frequently used as an optical element.
However, there are cases where even when a synthetic quartz glass body is used, the quantity of light passing through this glass body is small due to reflection by a surface thereof and this is regarded as problematic.
One example thereof is the exposure tool for semiconductor device production. In the exposure tool for semiconductor device production, synthetic quartz glass bodies are used as optical elements arranged between the laser light source and a wafer. However, in the optical elements through which the light passes, such as lenses, there are often cases where the amount of the light passing therethrough is small due to surface reflection and the amount of the light which finally reaches the wafer is considerably small. There is hence a desire for a highly transparent synthetic quartz glass body showing a minimized light quantity loss.
On the other hand, an excimer lamp is used in dry cleaning for removing organic contaminants from a display substrate or the like in liquid-crystal display production steps. In this case, ultraviolet light which has passed through a window made of a synthetic quartz glass yields atomic oxygen, which chemically reacts with organic contaminants present on the substrate to oxidize/gasify the organic contaminants and thereby clean the substrate. The larger the quantity of light with which the substrate is irradiated in this cleaning operation, the more rapidly the dry cleaning can be conducted. There is hence a desire for a window material made of a highly transparent synthetic quartz glass.
A highly transparent synthetic quartz glass body has hitherto been realized by forming an antireflection film made of a fluoride, e.g., MgF2, on the surface of a synthetic quartz glass body by a method such as vapor deposition or sputtering. However, this technique has had a problem that fluorine-deficient sites (sites where fluorine has been eliminated from the fluoride) formed in the antireflection film absorb light to reduce the light transmittance. There also has been a problem that the antireflection film has insufficient film strength and readily peels off upon an operation such as, e.g., wiping.
Patent Document 1: JP-A-60-36343 (Claims)
Patent Document 2: JP-A-59-232934 (Claims)
Non-Patent Document 1: Journal of Fluorine Chemistry, 2003, Vol. 122, pp. 81-86